Posted
by
Soulskill
on Saturday August 22, 2009 @11:27AM
from the george-carlin-would-agree dept.

BuzzSkyline writes "Despite fire codes that require emergency exits be clear of obstacles, some types of obstacles actually speed evacuation. The counterintuitive conclusion resulted from a series of experiments performed at a TV studio in Japan. Researchers from the University of Tokyo asked 50 volunteers to exit the studio through a narrow door. Video tapes of the experiments show that people made it out quickest when a pole was placed about 30 degrees to one side of the exit. The lead researcher believes an obstacle reduces jamming and friction among people in crowds by decreasing conflicts as the crowd presses toward the exit. A paper describing the research is scheduled to appear in the journal Physical Review E in September, but a preprint is available on the Physics Arxiv."

These guys [informs.org] already figured this out several years ago. (Sorry, I couldn't find a non-subscription link.)

During the pilgrimages to Mecca, one of the things that people are supposed to do is go into a large stadium and cast rocks at three pillars. Zillions of people attend this event, and there have been numerous trampling deaths at the entrance to the stadium. These guys showed that having obstructions near the entrance improves traffic flow, and so they recommended to officials in Mecca to install such obstacles there, resulting in far fewer trampling deaths near the entrance. Other means of traffic calming [spiegel.de] were used to mitigate deaths elsewhere in the stadium.

Actually though, if you give it a bit of thought, the result is not as counter-intuitive as you might think.

Basically, rather than having a flat wall with an exit that everyone bottlenecks up at, the pole acts as a "funnel wall" forcing people to line up earlier and more quickly. The same principle has been in use for hundreds of years with cattle and sheep. The "cattle gate" as we now call it, acts to slowly funnel stock animals into a single file line where they can be sheared, branded, loaded onto trucks, etc.

It just goes to show you that mammalian group behaviors are more universal than we might like to think.

The building codes try to increase exit width to handle higher traffic flow. The reality, at least as suggested by the research, is similar to what landscape architects have known for generations: people walk faster on a narrow sidewalk than a broad one.

In an emergency, you hit the maximum carrying capacity of any pathway. The key to evacuating a densely occupied space is to convince people to spread out to multiple different exit points, which is confusing in an emergency situation.

I don't think anything is perfect, but when people approach a single door from a number of different angles optimum traffic flow doesn't happen.

The weird thing is that people who actually design stuff for crowd control have known this since at the least the 1980s. The goal is to get people ordered into efficient lines heading towards the goals and make sure people understand the process is fair and nothing is to be gained by jumping lines. For a real world example, see Heathrow's newer terminals versus its older ones, or any third world airport: if you make it easy to cheat by changing lines, and other people can see you do it, you get a mob in short order. So, keep lines narrow, and hard to switch from one to another, and people move faster. That means barriers - big ones. Just think Disneyworld, airports, good stadia.

I'm sure policy varies by city / state, but in the city I drove for, there's footprints where you're supposed to put the door and people are supposed to wait. It's far enough back so they don't get whacked by the mirror as the bus pulls up (seen it happen!) and it helps elderly and children know where to go. Good drivers will usually hit it every time if they want to, but laziness, traffic conditions, and situation on the bus (someone standing unsteadily/in a bad spot such as down in the stairwell waiting to get off can make it easy to lose balance) can cause the driver to stop more slowly or more quickly than usual so as not to get rear ended and/or knock people over. In ideal conditions a driver should hit the prints every time. Substitute the footprints for a bus stop sign where applicable. The prints/sign are never directly in front of a shelter here as it makes it difficult for those that couldn't fit in the small shelter to got on the bus (maybe the shelters just aren't far enough back due to space?). People tend to line up just fine when you land on the spot. I've boarded 95 people on to a bus before and I've never really had a problem with people figuring out how to get on. Just my $0.02.